But this time the Porpoise did not move. It was as if she was up against a stone wall.
"What's the matter?" asked Mark, who had been awakened by the excitement on board.
"I do not know," replied Mr. Henderson gravely. "Something mysterious has occurred. We can go no further!"
CHAPTER VIII
ASHORE IN THE DARK
"Stop the engine," the captain commanded after he had peered through the lens in the conning tower for some time. "We must see what is the matter."
He glanced at the depth gage and noted that they were now four hundred feet below the surface. Then he consulted some charts.
"There is a depth of one thousand feet about here," he remarked. "Lower the ship, Washington. Let us see if by getting on the ocean bed we can get away from this obstruction."
The colored man opened wider the sea cocks by which the tanks were filled. The increased ballast sunk the Porpoise still lower, and, in a few minutes a slight jar told the navigators that they were on the bottom of the ocean.